Author: Phil Dixon
Date: 03:25:28 07/31/99
Go up one level in this thread
On July 30, 1999 at 10:46:28, Albert Silver wrote: >On July 29, 1999 at 19:44:55, Amir Ban wrote: > >>On July 29, 1999 at 09:29:32, Robert Hyatt wrote: >> >>>On July 29, 1999 at 08:25:58, Chris Carson wrote: >>> >>>>On July 29, 1999 at 07:16:32, Amir Ban wrote: >>>> >>>>>On July 28, 1999 at 18:16:24, Dann Corbit wrote: >>>>> >>>>>>On July 28, 1999 at 17:50:51, Kristo Miettinen wrote: >>>>>> >>>>>>>The position is the opening array, all pieces in their initial positions. The >>>>>>>explanation about the eight pawns makes sense, intending to steer Crafty into >>>>>>>open waters (on the assumption that the opponent is human?) >>>>>>> >>>>>>>I was looking into this on a whim, as I use the advantage of White in the >>>>>>>opening position as my quantum of positional value (on which scale the value of >>>>>>>a pawn is 6 quanta for me). >>>>>>Here is the C.A.P. record for that position. >>>>>> >>>>>>rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - acd 15; ce -7; pv e4 e6 Nf3 >>>>>>Bb4 Nc3 Ne7 Bc4 Nbc6 O-O O-O d4 Bxc3 bxc3 Na5 Bb5; pm e4; id "C.A.P. 4028"; >>>>>> >>>>>>I bet you never knew crafty was French. >>>>>> >>>>>>Crafty thinks it is behind by 7 one hundredths of a pawn. This is obviously >>>>>>conservative because white has a tempo at least. But I don't think that it is >>>>>>grossly inaccurate. >>>>> >>>>>A correct evaluation is one that matches the winning percentages of the >>>>>position. I think white has about 54% in serious play, and if so the evaluation >>>>>should be about +0.20. >>>>> >>>>>Amir >>>> >>>>Amir, >>>> >>>>Interesting point. If I read you correctly, the "Evaluation" should match >>>>the winning changes. This is not the way most programs "Evaluate" a position. >>>>Granted that a higher "Eval" by a program should mean a higher "Chance" to >>>>win, it is normally not a "Percentage" based on results. >>>> >>>>I have thought that this might be a better method of "Evaluation", some >>>>programs do use a "Percentage" (Crafty) for opening book moves, but not >>>>for middle game or end game positions. >>>> >>>>Any thoughts on how to incorporate "Percentage" into the "Evaluate" function >>>>of a program (knowledge)? Perhaps a "Percentage" "Evaluation" for positions >>>>and endgames as a part of the learning (Crafty might be able to do this) >>>>would be useful. Any comments? >>>> >>>>Best Regards, >>>>Chris Carson >>> >>> >>>I disagree. Evaluations are not 'absolute' any more than FIDE Elo ratings are >>>absolute. The correct evaluation is the one that lets you _win_ 54% (or better) >>>of the games from the opening position. Whether the starting score is +1.00 or >>>-1.00 is immaterial so long as you choose the best move(s) by using those >>>scores... >> >>This is to answer several posts in reply to my original comment: >> >>Evaluations need to represent winning chances in some way, or else there's not >>much use for them. It's true that the object of all this is to play good moves, >>but to say that is to beg the question of how to evaluate positions so as to >>play good moves. >> >>There are many ways to do this mapping. Obviously you can multiply the eval by a >>factor to choose your scale, and you can also add a constant without changing >>much, but an additive constant is suspect if you define a 0 evaluation to be >>equivalent to a draw or 50% outcome. As long as your mapping is monotone in >>winning chances, and your draw score is calibrated correctly, it's good. >> >>Practically, almost everyone agrees on scale by calling a pawn advantage about >>1.00 (on average). Assuming some smooth mapping (there are exponentials that are >>natural to use), to say that 54% maps to +0.20 is not so arbitrary as some >>commented, though if someone insists it's +0.15 or +0.30, I won't argue. A minus >>score, though, obviously doesn't fit because it has the wrong sign. >> >>The problem with having incorrect evaluations (not monotonic, or wrong sign) is >>obvious with some thought: the program may prefer a bad position to a good >>position (which always involves playing a bad move ...), or may accept a draw >>when ahead. >> >>Our evaluations may be bad regardless, because our knowledge of the game is >>incomplete, but there's no reason to accept a logical inconsistency in the >>evaluation. >> >>When I talk about winning chances I'm not referring to any specific database >>information that is available, but about an objective (and usually unknown) >>outcome of the position. >> >>Amir > >As for myself, I have problems with the comparison of statistics (winning or >losing percentages) with the eval. In the opening, you are judging it from the >results of games (where else can one dig up this 54% ?) which may have little to >do with the objective winning chances of the position. On the other hand, if you >get to an endgame with a slight edge, how do you calculate statistics on it? >Calculate every possible move and then balance out the number of winning moves >to the number of losing moves? Short of hitting the tablebases, I don't see how >this could be done, but since this CAN'T be done in a practical manner, thinking >along these lines is pointless. In the end, you may hit upon a point where the >best move objectively isn't necessarily the move that offers the opponent the >most chances to slip up. Imagine I have a position in which I have a slight >edge. Objectively, I have a move that should keep my edge though not necessarily >increase it, yet I have a complicated trap which renders all legal moves except >one losing. Statistically, this last option gives me the most winning chances, >yet it is hardly the best move, as if my opponent plays that one legal move, >I'll have lost my edge. Of course, if I have two options of equal value and one >of them places a trap, I should go for the trap, but what about when there is a >difference however small? When should you gamble? > > Albert Silver I think a little psychology (ala Lasker) should also be factored in. Phil
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